The exemplary embodiment relates to coating systems for structures in contact with water and finds particular application in waste water treatment and potable water systems.
Due, in part, to increasing environmental regulations and reduced or fluctuating water supplies in many areas, an environmentally friendly coating system is sought that can provide a variety of properties, such as excellent corrosion resistance, adhesion to a variety of substrates, excellent hydrophobicity, some flexibility, impact resistance, a relatively fast cure, and the ability to be applied in inclement weather conditions. It would also be advantageous to have a coating that can be used in both potable water and wastewater applications.
Existing coating systems while meeting some of these properties, often have limitations.
Epoxy coating systems provide excellent adhesion and corrosion protection in water and wastewater applications. However, most epoxy coating systems formulated for immersion conditions do not provide much flexibility. The lack of flexibility may result in “cracking” of the coating if the coated substrate has some movement. Furthermore, the cure speed of most epoxy coatings is slow resulting in delays while waiting for cure or to apply additional coats.
Polyurethanes provide good flexibility and can provide a fast cure speed. However, most polyurethanes do not perform well in wet or damp environments. This may be attributed to micro-foaming at the substrate surface due to the presence of water. The isocyanate portion of the reaction has an affinity or tendency to react with water faster than with the polyols and foaming is the result. This causes a loss of adhesion and some porosity in the coating.
Polyurea coating systems are well known for their speed of reaction, flexibility and ability to be applied in severe weather conditions. However, for maximum adhesion, most polyureas require a primer that can be applied only in favorable weather conditions. Further, some polyurea formulations are so fast curing that the resulting coating can have a sponge-like cell structure when viewed under a microscope. This structure can allow water (and other solutes) to pass through the coating much easier than some other coating systems.
There remains a need for a coating system that overcomes some or all of these problems.